A fuel pump used to provide fuel to an internal combustion engine may be driven by a lobed camshaft that displaces a tappet assembly, within a cylindrical bore, with a roller that rolls along the cam lobe. The reciprocating motion of the tappet assembly generates fuel flow that is used by the internal combustion engine to generate power. These types of fuel pumps are popular in modern fuel systems, and are frequently used in common rail fuel systems applications where high fuel pressures are required. In the prior art discussed below, the motion of the tappet assembly within the cylindrical bore is guided using a guiding member.
U.S. Pat. No. 7,568,461, issued to Straub, discloses a high pressure fuel injection pump having a roller tappet that includes a follower body that is received in a lower portion of a generally cylindrical guide sleeve. The follower body is fitted in an inner wall of the guide sleeve, which limits lateral motion of the roller and moves within the pumping cylinder with the follower body.
U.S. Publication No. 2007/0071622, filed by Schoeppe, discloses a high pressure fuel pump assembly having a roller tappet that includes a roller that is received by a rectangular shoe. The shoe travels within a guide path formed by the walls of an insert having a rectangular inner surface. The outer surface of the insert is cylindrical so that the insert can be disposed within a cylindrical opening of the pump housing.
U.S. Pat. No. 7,311,087, issued to Shaull et al., discloses a fuel supply pump having a tappet structure body that includes a shell, a roller body, and a roller. The shell includes an opening (slit) within which a guide pin slides to guide the movement of the tappet structure body within a cylindrical space in the pump housing.